The Battle of Terra was the penultimate battle of the Horus Heresy. Waged on Terra, the homeworld of humanity, the massive engagement between the forces of the Imperium of Man and the forces of Chaos decided not only the fate of Horus Heresy but also that of humanity.

The Storm Breaks

The siege of the Imperial Palace.

The Dark Mechanicum siege camps around the Imperial Palace

On the thirteenth day of Secundus, the bombardment of Terra began. From orbit, Horus' ships laid down an unrelenting barrage of missiles and energy beams. The first shell targeted the Sanctum Imperialis for symbolic reasons, though it did no damage and was quickly intercepted by many point defense systems. A vicious exchange of fire took place as the massive array of anti-ship gun batteries on Terra opened up on the traitor ships. Losses were incurred by both sides, but the traitor fleet in particular took heavy losses in space but endured through sheer weight of numbers.[9a] Horus' ultimate objective was the Imperial Palace, seat of the Emperor himself. The orbital bombardment was some of the most intense ever witnessed and shook even the courageous and battle-hardened loyalist Space Marines.[1b] However damage to the actual Palace itself was minimal due to a sophisticated multi-layered and self-repairing Void Shield system known as The Aegis as well as the fact that Terra's last orbital plate was placed over the Palace to serve as a shield and gun platform. However due to a reactor flaw in one of the Aegis' reactors, a small weakness appeared in the Palace network centered around Bastion outside the Helios Gate.[9a] Inside the depths of the Palace itself, the Emperor, attempting to keep the Golden Throne under control, could only brood over the desperate events occurring far above.[1b]

The bombardment continued for days as Perturabo probed for weaknesses in the Aegis, discovering the flaw around Bastion-16. The Aegis around this area was weakened enough to allow for slow-moving aircraft to penetrate. Despite the ragings of Angron and the boredom of Fulgrim, Horus would not launch an all-out attack yet. The Emperor's might not only prevented Daemons from manifesting on Terra, but also threatened to would destroy the Daemon Primarch's should they set foot upon its soil. Magnus and Zardu Layak surmised a ritual to eliminate the Emperor's barrier by spilling enough blood across Terra. Horus began to increasingly spend his time comatose, his spirit inside the Warp searching for lore as well as weakening the Emperor's spirit.[9b] After 12 days the bombardments continued, but were matched with the first ground assaults. Thousands of traitor vessels crashed into Terra's surface. Many were destroyed by the Palace defenses, but many more landed and unleashed endless hordes of Traitor Imperial Army, Beastmen, Cultists, and Mutants. These were largely distractionary measures to support the traitors true objectives as they ravaged the planet, as well as support the traitor aerial attacks on the Palace's anti-ship guns and void shield generators. The loyalists responded with their own aerial defenses, and massive dogfights erupted over the Palace as the conscripts outermost trenches around the walls held against the attacks by the Lost and the Damned. While the Palace held, elsewhere across Terra major population centers fell such as Lundun, Noy Zaylant Hive, Neork, and Braslya.[9l]

The pattern of orbital attack, landings by traitor rabble, and aerial assault repeated itself for weeks before the Death Guard fleet under the now-corrupted Mortarion arrived at Terra. True to his earlier word to let Mortarion's legion be the first to set foot upon Terra, Horus prepared to use the Death Guard in the first Astartes-led assaults on the Palace.[9d] This caused Angron to rage, and to prevent him from destroying his own flagship The Conqueror he was teleported by World Eaters 8th Company CaptainKharn into the ever-shifting labyrinth originally built for Vulkan aboard the Night Lords flagship Nightfall.[9f] On the seventh of Quartus the first Death Guard Drop Pods landed on Terra's soil as the Nine Disciples of Kelbor-Hal each beached one of their Ark Mechanicus-class Battleships around the Palace. The Void Shields and bulk of the Ark Mechanicus vessels allowed for the traitors to establish their first real footholds around the Palace, and as the Death Guard unleashed gas and plagues upon the trenches around the walls the Dark Mechanicum set about their work of constructing siege engines.[9e] The Death Guard assault on the outermost trenches around the Palace was about to break the Imperial Army defenders until Jaghatai Khan, defying Dorn's orders to remain in the palace, led a Jetbike charge by the White Scars. The Scars pushed past the traitor frontline into their siege camps before the Khan was finally forced from his Jetbike. Jaghatai slew dozens of Death Guard until he was wounded by a Warp-tainted poisoned blade. Ultimately Sanguinius had to sortie out of the Palace with his Sanguinary Guard to rescue Jaghatai, who recovered from his Warp sickness as soon as he began to move closer to the Sanctum Imperialis and the psychic might of the Emperor. The Khan's move was not reckless however, he also gathered valuable intelligence on the siege engines the traitors were constructing.[9g] Meanwhile aboard the Vengeful Spirit, Horus finally allowed Perturabo to begin his preparations to clear landing zones around the Palace for their Titans.[9h]

On the Fifteenth of Quartus, the traitors initiated their dual plan to break The Aegis and allow for the manifestation of Daemons upon Terra. A giant projected face of Zardu Layak appeared on an island of bones which descended from the sky, urging the commoners of Terra to rise up against the Emperor and ensuring them that if they turned to Horus now they would be spared. The Palace guns could not silence the corporeal island, and after his speech concluded it began to rain blood. The blood signaled that the traitors had finally undertaken their ritual to weaken the Emperor's psychic barrier, and the Mechanicum released their Daemon Engines. Eight "Warp-Bane" guns constructed near the sites of the beached Ark Mechanicus vessels opened up on the Aegis Shield around the Palace, sapping it of its energies as the Death Guard deployed massive Towers of Nurgle at the walls. As the Aegis gave way the traitor bombardment finally was able to hit the Palace defenses directly, causing massive devastation and allowing for a Night LordsRaptor assault on the Eternity Wall. The outermost trenches around the Palace Walls were now untenable, but Sanguinius opened up the Helios Gate and led a massive counterattack by the Blood Angels and Imperial Fists as well as Titans of the Legio Solaria. Sanguinius knew victory was impossible, but had his Astartes buy enough time to allow for the Imperial Army conscripts to make it inside the walls and allow for Titans to destroy the incoming Towers of Nurgle.[9i] On top of the eternity wall itself, Blood Angels First Captain Raldoron bested the acting Night Lords commander Gendor Skraivok and threw him from the Walls.[9j] It was in this maelstrom of destruction that Angron himself fell from the sky, having been released from the bowels of the Nightfall. After massacring his way through friend and foe alike to the Eternity Wall Angron bellowed a challenge to Sanguinius, who saluted his fallen brother and stated that while they would battle one day, today was not that day. Angron raged, but could not proceed any further due to the lingering effects of the Emperor.[9k]

Battle for the Palace

As the battle continued to be waged, the Eternity Wall and Lions Gate Spaceports fell to an overwhelming assault by World Eaters and KhornateTitans led by Angron.[2] With a landing fields now in his hands, Horus was able to land his Titans and heavy war engines.[1b] Within a few scant hours the forces of Horus managed to seize control of the spaceports of the Imperial Palace and kill tens of thousands of loyalist warriors, the assault itself led by the World Eaters, Thousand Sons, and Emperor's Children under the personal command of Angron. Supported by Titans and overwhelming numbers of traitorous Imperial Army, Cultists, Daemons, and Mutants, the traitor forces managed to surround its entire circumference.

Horus ordered his army to push on and had the attack on the outer walls of the Imperial Palace be spearheaded by the Death's Head Titan Legion. Losing five Titans within minutes to entrenched loyalist defenses, the traitor forces would not relent and kept hammering away at the palace walls. A counterattack against the Chaos horde's flanks by loyalist titans failed, though the White Scars took advantage of the confusion it caused to sweep down at the traitor forces rear columns and wreak havoc.[2] The Siege of the Imperial Palace soon ground on for many days, with the two primary attacks during this time being made by Angron and his World Eaters supported by Daemon Engines in one sector and the Legio Mortis commanded by Iron Warriors Primarch Perturabo in the other. The Emperor's Children, led by Fulgrim, soon became bored of the stalemate and set off on a bloody orgy against the people of Terra of such depravity and destruction that ten thousand years later, Terrans are still distrustful of Space Marines.[1c]

Meanwhile, while the traitor army had been battering at the Palace walls, Jaghatai Khan and his White Scars Legion had been busy harassing their flanks in a series of hit-and-run attacks. Now the Khan changed plans and launched a lightning nightime raid on the Lions Gate spaceport in cooperation with the 1st Terran Tank Division of the loyalist Imperial Army, easily overrunning the traitor garrison and reclaiming the port in the name of the Emperor. The attack managed to slow the Traitor advance on the Imperial Palace.[1c] In addition, Horus ordered the Death Guard to pull back from the assault on the palace to deal with the White Scars.[2]

Under Perturabo's command, a combined assault was launched that finally saw a traitor breakthrough. Perturabo combined an underground assault in tunneler drills with a pinpoint Chaos titan Macrocannon bombardment.[2] The walls of the Emperor's Palace finally broke, unleashing a flood of traitors into the inner courtyards of the Palace. A massive labyrinth of hallways, complexes, courtyards, and buildings, fighting in the outer palace was room-to-room and saw heavy casualties inflicted on the Traitors.[2] Moreover, the inner sanctum of the palace had been heavily reinforced and in the enclosed spaces Traitor titans and heavy war engines became easy prey for the well-prepared loyalists. The Adeptus Custodes made a fierce counterattack at the inner gardens of such brutal efficiency that none of the traitor horde could initially stand against them. However in the end, the Titans of the Legio Mortis proved decisive in a traitor breakthrough. In addition traitor numbers were too great and even the Custodes were overwhelmed. After inflicting horrendous casualties on the traitor forces, so much so that the Chaos Titans could no longer continue to advance,[2] the Custodes would fall back to the final defensive line around the Imperial Palace, the Eternity Gate, manned by the Blood Angels and their Primarch Sanguinius. Perturabo and his Iron Warriors thought that their job had been done, and the Primarch left the battle for the Inner Palace to instead direct a siege against the Imperial FistsFortress Monastery nearby.[2]

Meanwhile, Magnus the Red and the Thousand Sons finally joined the battle on the Traitor side, attacking the Ultimate Gate of the inner sanctum of the Imperial Palace in conjunction with a horde of Khorne Daemons and World Eaters.[2] As traitorous hordes swarmed towards this final bastion of defense, Sanguinius himself became locked in mortal combat with a mighty Bloodthirster of Khorne, Ka'Bandha, the daemon he had battled at Signus Prime. After a protracted and bloody airborne struggle above the Ultimate Gate, the Primarch broke the Daemons back over his knee.[1c] The defending Blood Angels and Custodes forces were reinforced by the Imperial Fists led personally by Rogal Dorn, which disembarked from the great Sky Fortress, a massive fortified orbital plate. Though it managed to deliver withering fire and much-needed reinforcements to the loyalist forces and stopped an attempt by Thousand Sons Sorcerers to destroy the inner sanctum in an arcane ritual[2], in the end the Sky Fortress was shot down by the Titans of the Death's Head legion. The ensuing crash detonated the ships great plasma reactors, creating an explosion that ripped a forty three kilometer wide crater outside the palace. Though the blast had wiped out massive numbers of traitors, the loyalist forces now realized that they were cut off from the rest of Earth.[1c]

The Vengeful Spirit

However despite these gains, the situation soon changed for the worse for Horus. He recieved news from his daemonic allies that the Space Wolves and Leman Russ had evaded the Alpha Legion, the Ultramarines under Roboute Guilliman had defeated the Word Bearers at Calth, and the Dark Angels under Lion El'Jonson were also Terra-bound. Horus was furious at the news. He had gambled everything on being able to defeat the forces of Terra before the Emperor could muster help from all the still-loyal Legions. With time against him, it now appeared that the gambit had failed and came up with an even riskier gambit. Lowering the teleportation-inhibiting Void Shields on his Battle Barge, Vengeful Spirit, Horus in effect invited the Emperor to come to him.[1d]

Despite objections by Rogal Dorn, the Emperor decided to willingly fall into Horus' trap knowing all to well what awaited him. Leaving management of the Golden Throne to his trusted subordinate Malcador, the Emperor, Dorn, Sanguinius, as well as an elite force of Space Marine Terminators and Adeptus Custodes teleported directly into the Vengeful Spirit. However the teleportation process had malfunctioned and the loyalist forces were scattered throughout daemonically corrupted ship.[1d]

Coming under attacks from all kinds of horrors aboard Horus' flagship, including Daemons, monsters, and Chaos Space Marines, the loyalist forces fought their way across the Battle Barge in search of Warmaster Horus himself. The first to reach the traitorous Warmaster was Sanguinius himself. Refusing a final offer by Horus to join him in his campaign against the Emperor, the heroic Primarch found himself completely outmatched by the Warmaster, now warped by the powers of Chaos, and was struck down.[1d]

When the Emperor finally reached Horus, he witnessed to his horror the mauled corpse of Sanguinius at the traitorous Warmasters feet. Overwhelmed by sorrow, the Emperor was speechless as Horus mocked his once-beloved father, proclaiming himself the rightful ruler of humanity and claiming to have even bound the Chaos Gods to his will. The Emperor could only look on in pity, knowing all to well the trap that had ensnared his son. Stating that Horus had become a slave to Chaos, not the other way around, Horus became enraged and the great duel to decide the fate of humanity finally began.[1d]

Horus and The Emperor meet for their final battle

Though a Psyker of unparalleled might, even the Emperor found himself greatly challenged by the might of Horus and the Chaos energies that swelled within him as the two engaged in a titanic battle of not only Power Sword and Lightning Claw but also psychic power. However even after all that he had done, the Emperor could not bring himself to use his full power and risk killing his beloved son. Using the immense power he had acquired during the Battle of Molech and imbued with the energies all four Chaos Gods, Horus crushed the Emperor's windpipe, severed the tendons of his wrists, broke most of his ribs, plucked out his left eye, and set his hair alight. As if this weren't enough, Horus lifted the Emperor high above his head and brought him down upon his knee, crushing the Emperor's spine. Further punishing his father by ripping one of his arms from its sockets, Horus howled over the beaten body of the Emperor in triumph.[1d]

But suddenly, the beating stopped. A lone Custodian of the Adeptus Custodes had entered the room (while other sources state it was Ollanius Pius, an Imperial Army soldier). Without hesitation, the loyal warrior had charged towards Horus. Breaking out in laughter, the Warmaster blasted apart the warrior in a gaze of psychic energy. This proved to be the decisive moment in which the Emperor finally realized what his son had become. The Horus he had known was truly gone, destroyed by the maddening powers of Chaos. Realizing that he must kill Horus and he would never get another chance, the Emperor used the brief respite to lash out at Horus with his full power. Focusing his psychic bolt into a bolt of pure force, the lance of power blasted straight through the Warmasters heart. Realizing their pawn had failed, the Gods of Chaos retreated from Horus' body. As they did, sanity returned to the Warmaster. In that moment, Horus, realizing the atrocities he had committed, begged the Emperor to strike the finishing blow before the powers of Chaos would take hold over him once more. Focusing the last of his strength into another psychic bolt, the Emperor finally destroyed his repentant son.[1d]

Rogal Dorn and his Terminator escorts would reach the chamber shortly after, discovering the beaten body of the Emperor alongside the remains of Sanguinius and Horus. The Emperor only had enough strength to demand to be taken to the Golden Throne at once. Obeying his beloved master, Dorn and the surviving loyalist forces teleported off the Vengeful Spirit and back to the Imperial Palace. Meanwhile the death of their Warmaster had sent a psychic shock reeling across the traitorous armies on Terra. As the Great powers of Chaos retreated from Horus they took their Daemonic hordes with them. Confusion broke out among the traitor Primarchs and the rebel armies lost all cohesion. It was said that the Sons of Horus, sensing their father's death, immediately broke and were the first to flee from the planet[5] while Mortarion and the Death Guard were the last.[6]

At the same time, the Blood Angels began suffering horrific visions of the death of Sanguinius. In what may be the first instance of the Black Rage, the Blood Angels broke ranks and began engaging the traitors in close combat with such savagery it shocked both loyalist and traitor Marine alike. Using this to their advantage, the loyalist forces led a decisive counterattack which finally expelled the traitorous legions from Terra in a bloody rout.[1d]

Aftermath

Though Horus had been slain and the traitorous forces driven from Terra, tragedy was not yet over for the Imperium. Malcador had been reduced to a pile of dust from the strain of controlling the Golden Throne and the Astronomican in the Emperor's absence, and the dying Emperor himself was adamant that he himself be hooked back up to the arcane machine. Issuing his last spoken words to his most trusted followers which had gathered around him, the Emperor left the fate of humanity in the hands of his remaining Primarchs. Becoming silent, for the last ten thousand years he has remained interned on the Golden Throne, sustained by its advanced technology and the daily sacrifice of a thousand psykers.[1e]

The Horus Heresy did not end with the Battle of Terra. The Loyalists still had to drive the remaining rebels from the Imperium, one world at a time. In what became known as the Great Scouring, the traitorous forces of Chaos were eventually driven into the Eye of Terror.[1e]

Canon Conflict

In the original lore, Lorgar himself led the Word Bearers on Terra. However as of the events of the novel Slaves to Darkness, Lorgar is banished from Horus' sight for attempting to usurp him and instead the Word Bearers at Terra were led by Zardu Layak.[4]